###Compression###
* What type of compression is available in ACS ?
When HRC is prime and WFC is the auto-parallel, the buffer
dump for the WFC parallel may occur during the next exposure.
A WFC buffer dump takes ~6 minutes, and most HRC prime exposures
will not be long enough to include both the WFC auto-parallel
and its associated buffer dump before the the HRC exposure ends.
When this occurs both images will be in the buffer at the same
time and since the WFC is not the prime science, one of the four
WFC quadrants will be compressed. Also, any data loss in the WFC
auto-parallel due to compression is considered routine and those
observations will not be repeated.